A conventional high frequency coil of the above kind is shown by way of example in the form of a wiring diagram in FIG. 4, wherein an input side coil and an output side coil electromagnetically coupled together are provided. The input side coil is divided into two coil elements L11 and L12 having substantially the same inductances by the provision of a center tap 1. To these coil elements L11 and L12, tuning capacitors C11 and C12 are connected respectively in parallel, thereby providing two like tuning circuits of the same frequency. A signal is applied, together with a local oscillator signal, to terminals 2 and 3 arranged at the ends of the input side coil, and a frequency-converted or more specifically as an intermediate frequency signal is obtained from the output side coil L2. Additionally, the tap 1 is grounded.
It is a most important requirement to couple both coil elements L11 and L12 with output side coil L2 in the same manner, to provide the same transmission characteristics thereamong and to reduce a frequency difference between the two tuning circuits to nil.
Adjustment of the two tuning circuit frequencies is carried out conventionally by moving cores arranged in close proximity to related coils, so as to modify the respective inductances. However, when the overall dimensions of the high frequency coil assembly are highly minimized so as to arranged the within a cube of less than 4 mm on a side, the conventional arrangement is not practical due to realizable mechanical machinability and strength requirements of the cores.